<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="app">
        Hello
    </div>
    <script>
        let data = {
            msg: 'Hello',
            count: 0
        }

        let vm = new Proxy(data, {
            get(target, key) {
                console.log('get, key', key, target[key])
                return target[key]
            },
            set(target, key, newValue) {
                console.log('set,key', key, newValue)
                if (target[key] === newValue) {
                    return
                }
                target[key] = newValue
                document.querySelector('#app').textContent = target[key]
            }
        })
        vm.msg = 'Hello World'
        console.log(vm.msg)
    </script>
</body>

</html>